Gangs were likely involved in the string of arson attacks, police said, and they come amid mounting concerns in Sweden about gang-related violence. More than 40 people were shot and killed in the Nordic country last year, and the prime minister said in January that he was not ruling out a military response to gang activity.

A rooftop camera recorded the silver Ford Fiesta driving past Parliament and suddenly veering sharply to the left, striking cyclists waiting at a set of lights, then crossing the road and crashing into a barrier outside Parliament. Armed police surrounded the car within seconds, pulling a man from the vehicle. Police said the driver was alone and no weapons were...